1. Field of the Invention
The present invention relates to an optical recording apparatus, particularly to one such as a laser printer or a copier that perform optical recording by modulating and scanning a plurality of laser beams.
2. Description of the Related Art
Jp 10-197837A discloses one of the related art, which is described below with reference to FIG. 16. A multi-channel optical modulating apparatus in JP 10-197837A comprises a laser light source 2-1, a beam expander 2-3, a diffraction grating 2-9 by which the laser beam 2-2 issued from the laser light source 2-1 and passing through the beam expander 2-3 is split into five laser beamlets 2-4xcx9c2-8 spaced apart by an angle of xcex8, a condensing lens 2-10 for collimating and condensing the laser beams 2-4xcx9c2-8 issued from the diffraction grating 2-9, and a 5-channel acousto-optic modulator 2-16 for independently modulating the laser beams 2-11xcx9c2-15 emerging from the condensing lens 2-10.
The condensing lens 2-10 and the diffraction grating 2-9 are spaced by a distance equal to the focal length f2-10 of the condensing lens 2-10, and so are the condensing lens 2-10 and the acousto-optic modulator 2-16.
However, as regards the disclosed multi-channel optical modulating apparatus, JP 10-197837A has no explicit statement of the conditions under which the diffracted beams 2-4xcx9c2-8 obtained by splitting with the diffraction grating 2-9 are incident on the condensing lens 2-10. In addition, no mention is made of the optics for the light exiting from the acousto-optic modulator. Therefore, depending on the case, the series of spots formed by allowing the laser beams 2-11xcx9c2-15 from the condensing lens 2-10 to be condensed on the acousto-optic modulator 2-16 may sometimes be curved. As a consequence, the ultrasonic waves used to perform optical modulation within the acousto-optic crystal in the acousto-optic modulator 2-16 will have time delays before they reach the individual spots of condensed light; what is more, when a plurality of beams are scanned over a photosensitive material placed subsequent to the acousto-optic modulator 2-16, an error will be introduced in the distance between adjacent scanning lines.
Therefore, an object of the present invention is to ensure that no curvature will be introduced in the series of spots formed by allowing the individual laser beams from the condensing lens to be condensed on the acousto-optic modulator. Another object of the invention is to provide an optical recording apparatus with which the spots of condensed light on the acousto-optic modulator can be imaged on a surface of interest to perform scanning with a plurality of beams without introducing an error in the distance between adjacent scanning lines.
The objects of the invention can be attained by an optical recording apparatus comprising a light source which issues laser light, a light-transmitting diffraction grating by means of which the laser light issued from said light source is split into a plurality of diffracted light beams, a multi-channel acousto-optic modulator which modulates said plurality of diffracted light beams being sent from said light-transmitting diffraction grating, an imaging lens provided on the optical path between said light-transmitting diffraction grating and said multi-channel acousto-optic modulator, and a rotating polygonal mirror by means of which the plurality of laser beams being sent from said multi-channel acousto-optic modulator are scanned in a given direction with respect to the surface being scanned, said light-transmitting diffraction grating being provided at the front focus of said imaging lens and said multi-channel acousto-optic modulator being provided at the back focus of said imaging lens, characterized in that said multi-channel acousto-optic modulator is provided on said optical path in such a way that the individual channels thereof are arranged substantially horizontally.